1. Field of the Invention (Technical Field)
The present invention relates generally to the field of gasoline and diesel-powered internal combustion engines that make use of exhaust gas recirculation (EGR) systems and, more particularly, to dual and hybrid EGR systems that are specially adapted for use with turbocharged internal combustion engines.
2. Description of Related Art
EGR is a known method that is currently employed with internal combustion gasoline and diesel-powered engines for reducing NOx emissions. Conventional EGR systems work by taking a by-pass stream of engine exhaust gas from an engine exhaust manifold and directing the same to a control valve or an EGR valve. The EGR valve is designed and operated to provide a desired amount of exhaust gas for mixture with intake air and injection into the engine's induction system for subsequent combustion. The EGR valve regulates the amount of exhaust gas that is routed to the engine induction system based on engine demand.
The process of recirculating the exhaust gas insures that partially-oxidized NOx becomes fully oxidized, thereby reducing smog producing partially-oxidized NOx emissions. Accordingly, such convention EGR systems include exhaust by-pass tubing or piping, related plumbing and manifolding, and engine driven EGR pump (if further pressurizing is necessary), and an EGR control valve, all of which are ancillary components that are attached to the engine.
While such conventional EGR systems may be sufficient for meeting today's emissions regulations for certain application, future emission requirements will be more stringent and the current state of the EGR technology will not be able to meet such requirements. For example, starting in the year 2007, medium and heavy-duty on-highway diesel emissions regulations will require that the amount of nitrogen oxide gases (collectively known as NOx) emitted be reduced by an order of magnitude (10×). Such reduction in emissions may possibly be achieved via EGR and/or by exhaust gas after-treatment.
When looking at turbocharged engine applications, such as in the case of a turbocharged diesel-powered engine, the use of these combined methods make it more difficult than ever to match the turbocharger operation to provide optimum engine performance while still maintaining the ability to provide sufficient EGR driving (i.e., negative engine ΔP) capability.
It is, therefore, desired that an improved EGR system be provided in a manner that is adapted for use in turbocharged engine applications to provide the same or improved engine performance characteristics, when compared to conventional EGR systems, while also meeting the increasingly stringent emission requirements described above.